Core features:
* you feel like an Emperor, not a logistics officer or a planetary manager (audiences, imperial court, managing imperial officials, rebellions, assassination attempts)
* no micromanagement, an epic scale with hundreds planets under your control yet you are not bogged down by boring micro (and I don’t mean automated AI governors), also late game is not drastically longer than the early game (game not dragging on at late stages)
* asymmetric gameplay, the AI plays by different rules than the player, races are not equal, different starting conditions
* hierarchical fleet, you do not move individual ships around but deal with whole formations

Minor features:
* you do not start in an empty galaxy, most of the galaxy is already colonized
* optional game modes where you start with having like half of the galaxy under your control and then you try to fight off rebels and other “late start” modes
* storyline system (plots to overthrow the Emperor, discovering legends of ancient races, etc)